1. Field of the Invention
The application relates to a method and a related communication device used in a wireless communication system and related communication device, and more particularly, to a method of designing a reference pattern and a related communication device in a wireless communication system.
2. Description of the Prior Art
A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) and communicates with a plurality of mobile stations, also referred as user equipments (UEs).
A long term evolution-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system, considering relaying for cost-effective throughput enhancement and coverage extension. The LTE-A system includes all of the features of the LTE system and several new ones, the most important of which are: carrier aggregation, enhanced multi-antenna support and relaying. The LTE system provides extensive support for deployment in spectrum allocations of various characteristics, with transmission bandwidths ranging from 1.4 MHz up to 20 MHz. In the LTE-A system, the transmission bandwidth can be further extended with carrier aggregation wherein multiple component carriers are aggregated and jointly used for transmission to/from a signal UE. In general, up to five component carriers can be aggregated, allowing for transmission bandwidth up to 100 MHz. In addition to wider bandwidth, LTE-A system is also expected to provide higher data rates and improved system performance. It will do this by further extending the support for multi-antenna transmission compared to the first release of LTE. For the downlink (DL), up to eight layers can be transmitted using an 8×8 antenna configuration. This allows for a peak spectral efficiency exceeding the requirement of 30 bits/s/Hz and implies a possibility for data rates beyond 1 G bit/s in a 40-MHz bandwidth and even higher data rates with wider bandwidth.
Technology for supporting reliable and high-speed data service includes Orthogonal Frequency Division Multiplexing (OFDM), Multiple Input Multiple Output (MIMO), and so on.
An OFDM system is being considered after the 3rd generation system which is able to attenuate the ISI effect with low complexity. The OFDM system converts symbols, received in series, into N (N is a natural number) parallel symbols and transmits them on respective separated N subcarriers. The subcarriers maintain orthogonality in the frequency domain. It is expected that the market for mobile communication will shift from the existing Code Division Multiple Access (CDMA) system to an OFDM-based system.
In order to carry out coherent demodulation in LTE down link, channel estimation is needed at the receiver end. In case of OFDM transmission known reference symbols are added into time-frequency grid for channel estimation. These signals are called LTE Downlink Reference signals. DL reference signals are exploited for downlink channel estimation for coherent demodulation/detection, downlink channel quality measurements, and cell search/acquisition. Different DL reference signals have been introduced in Release 10. A cell-specific RS is transmitted in each physical antenna port. It is used for both demodulation and measurement purpose. Its pattern design ensures channel estimation accuracy. LTE-A eNB should always support LTE UE as well. It is also used for LTE-A UEs to detect PCFICH, PHICH, PDCCH, PBCH, and PDSCH (transmit diversity only). A demodulation reference signal (DM-RS) are supported for transmission of PDSCH and transmitted on antenna port (s), or, where is the number of layers used for transmission of the PDSCH. The DMRS can be precoded, and supports non-codebook-based precoding. It will enable application of enhanced multi-user beamforming, such as zero forcing (ZF) for 4×2 MIMO. The DMRS pattern for higher numbers of layers is extended from a 2-layer format for transmission mode 8 in Release 9.
In OFDM systems, assigning a reference signal to all subcarriers is performed in order to achieve the performance of channel estimation. Reference signal patterns should be designed with small overhead and satisfactory channel estimation performance for control signals.